The specific aims of this proposal are to establish the general histamine levels found in the ocular tissues of albino rabbits by the use of a sensitive fluorometric assay. Also, extensive work will be done to establish the purity of this assay. Work will be done to establish that the choroidal/pigment epithelium histamine concentration follows the predictable but varying mast cell distribution in this tissue (between the optic nerve and iris). Once established, these tissue levels will be used to measure responses to inflammation and histamine releasing agents.